Demolition Hammer: Bad Vibration

A worn armature housing bearing can cause this symptom. Listen for a grinding, humming or whining noise – these are all signs of a bearing starting to go. The following repair procedure will vary on different models, but will be similar.
Remove the handle from the unit. Take out the screws that are securing the housing for the motor and remove from the unit. Next, pull the armature out of the housing. Remove the armature from the bearing housing by placing it in a vice. Using a spanner wrench, spin the cap on the back or place a punch in the side of the notch. Now, tap it with a hammer to spin it loose. Remove the nut located underneath the cap. Using a puller, place it over the bearing housing with the center on the shaft and remove. At this point, the fan and brush ring will lift off.
With the armature bearing housing removed, use a socket and a hammer to tap the bearing out of the housing. Press the new bearing in with a socket and a press. If you do not own a press, use a socket big enough to go on the outside of the race (on the bearing) and gently tap it in place with a hammer to avoid any damage.
To replace the armature bearing, place the armature in a vice and use a bearing puller to remove the bearing. Install the new bearing using a socket big enough to go on the outside of the race. Gently tap in place with a hammer.
Reinstall the fan and brush holder in the bearing housing. Ensure the tabs line up with the brush holder. Place the armature in the housing and reinstall the nut. Place in a vice to tighten. Spin the cap back on and ensure it is tightened. Slide the armature back on the housing the same way you removed it then reattach the housing assembly to the unit and secure the screws tight. Reattach the handle.

If the handle is broken, it will cause a bad vibration as its structural integrity has been weakened. With just a simple visual inspection, a broken handle will jump out at you. To replace the handle, remove the screws securing it to the unit and pull the handle off. On some models, it is as simple as installing a new handle. You may have to transfer the springs over first, then reinstall the handle back on the unit. On other models, you will have to remove the switch and power cord from the handle, transfer it over to the new handle and then install the new handle on the unit.

The springs are located inside the handle and take the brunt of the vibration caused by the hammer in operation. This makes it easier on your hands and arms. If the springs are weak, worn or broken, you will get a bad vibration. To check for this, remove the screw securing the handle and then remove the handle from the unit. Next, remove the springs from inside the handle and inspect them for any signs of breakage. If the springs look good, but the unit is old, or often used, replace them with new springs to get rid of the vibration. Replacing your springs will also restore the anti-vibration system to new condition. If the unit is older, with one broken spring, replace them all. If it is a newer unit, with one broken spring, you should be okay with just replacing the damaged spring. On a newer machine, the rest of the springs should still be in good condition. Once you have replaced the springs back in the handle, reassemble the handle back on the unit, with the screws secured tight.